Progress in the field of nano-technology enables the fabrication of devices having smaller and smaller structural elements. For the processing and the representation of nano-structures, tools are required which are able to scan these structures in several dimensions so that an image can be generated from the measurement data.
In a scanning particle microscope, a particle beam interacts with a sample. Scanning particle microscopes are in the following abbreviated as SBM (Scanning particle Beam Microscope). For example, electrons and/or ions are used as particles. Other particle beams can also be used, such as, for example, atom beams or molecule beams. Using electron beams or ion beams, large areas of a sample can be scanned with an adjustable resolution. Thus, scanning particle microscopes are powerful analysis tools in the nano-technology.
These tools can provide limited topographical information of the sample surface in the direction of the particle beams. In many application fields of the nano-technology, it is useful to precisely know the height profiles of a sample surface.
On the other hand, scanning probe microscopes scan a sample or its surface with a test prod, and thus generate a realistic topography of the sample surface. In the following, a scanning probe microscope is abbreviated by SPM (for Scanning Probe Microscope). Various types of SPMs are differentiated by the kind of interaction between the test prod and the sample surface, as for example scanning tunneling microscopes (STM) and scanning force microscope (AFM for Atomic Force Microscope or SFM for Scanning Force Microscope).
Scanning probe microscopes can scan the sample surface with a resolution up to the atomic range depending on the used test prod. However, the large resolution limits the application of these tools to very small sections of a sample.
Already some time ago, these considerations have led to the idea to use both tools for the analysis of a sample. For example, the authors Ch. Gerber et al. describe in the article “Scanning tunneling microscope combined with a scanning electron microscope”, Rev. Sci. Instr., Vol. 357, No. 2, pp. 221-224 (1986) to combine scanning particle microscopes and scanning probe microscopes in one apparatus. In a simultaneous operation, these tools shall simultaneously investigate one position of a sample in order to bring into effect the benefits of the respective tool and to avoid to a large extent the discussed drawbacks of each tool.
The development has been started from both sides. For example, the authors A. Emundts et al. describe in the article “Combination of a Besocke-type scanning tunneling microscope with a scanning electron microscope”, Ref. Sci. Instr., Vol. 72, No. 9, pp. 3546-3551 (2001), the insertion of an electron gun and a respective detector in a scanning tunneling microscope. The authors A. Wiesner et al. exemplarily explain the subsequent insertion of a scanning tunneling microscope in a scanning electron microscope in the article “Design consideration and performance of a combined scanning tunneling and scanning electron microscope”, Ref. Sci. Instr., Vol. 68, No. 10, pp. 3090-3098 (1997).
The Japanese application JP 2009 148 889 A discloses a combination of a focused ion beam (FIB) device and a force microscope. The sample stage of the combined tool has a tilting device which allows aligning of the sample in the direction of both analysis systems.
When combining a scanning particle microscope and a scanning probe microscope, several partially fundamental problems appear. A space problem inevitably occurs when combining both analysis tools in one vacuum chamber. Therefore, due to construction problems often a trade-off is made with respect to the performance of both tools. For example, the number of detectors is limited which can be used for analyzing particles released by the particle beam of the scanning particle microscope from the sample.
Another important issue is the mutual interaction of the two analysis tools when they are simultaneously in operation. For example, the tip or the test prod of the probe can partially shadow the particle beam, and thus restrict its field of view. The article “Transparently combining SEM, TEM & FIBs with AFM/SPM & NSOM” in the product brochure Nanonics, Issue 2.3, December 2002, describes the application of specifically developed glass probes for the scanning probe microscope in order to reduce the shadowing effect with respect to the particle beam. The described disadvantages can be avoided to a large extent by dropping the requirement that the SBM and the SPM simultaneously investigate the sample at the same position. Such a combination of the two analysis tools is described in the PCT application WO 2012/163 518 of the applicant. As a result, the trade-offs in the performance enforced by space problems of a SBM and a SPM and their combination in an apparatus can be avoided.
If the two tools investigate the sample spatially separated from each other, the distance of the positions at which the respective analysis tool scans the probe have to be exactly known. Already the change of one or several parameters of the SBM however leads to a small change of the point of impact of the particle beam on the sample surface.
As a consequence, a re-calibration of the SBM, i.e. a change of one or several parameters of the SBM, requires a re-determination of the distance between the SBM and the SPM. Such a measurement process is time consuming. It requires either inserting a measuring stick into the apparatus or shifting one of the two analysis tools into the operating range of the other one, if this is possible. Both alternatives reduce the sample through-put.